Field of the Invention
The present invention relates to an organic light emitting display device, and more particularly, to an organic light emitting display device for adjusting a threshold voltage shift.
Discussion of the Related Art
Flat panel display devices in related art are becoming thin and light and have low consumption power. Liquid crystal display (LCD) devices included in flat panel display devices include a thin film transistor (TFT) and have high quality resolution, color display, and image quality. Liquid crystal display devices are commercialized for notebook computers, tablet computers, and desktop computers. In particular, organic light emitting display devices are self-emitting devices, and have a fast response time, low power consumption, high emission efficiency, and a wide viewing angle.
FIG. 1 is an exemplary diagram schematically illustrating a related art organic light emitting display device. The related art organic light emitting display device includes an emission unit OA including an organic light emitting diode OLED and a pixel circuit unit CA that includes a first switching transistor ST1, a second switching transistor ST2, a driving transistor DT, and a capacitor Cst which drives the emission unit OA.
The pixel circuit unit CA includes a data line DL through which a data voltage Vdata is supplied to the first switching transistor ST1, a gate line GL through which a scan signal Scan is supplied, a power line PL through which a first driving voltage Vdd is supplied to the driving transistor DT, a sensing signal line SL through which a sense signal Sense is supplied to the second switching transistor ST2, and a reference voltage line RL through which a reference voltage Vref is supplied. The organic light emitting diode OLED included in the emission unit OA is electrically connected between a source of the driving transistor DT and a cathode voltage Vss terminal. The organic light emitting diode OLED emits light with a data current Ioled supplied from the driving transistor DT.
The pixel circuit unit CA includes a light blocking layer 20 which is formed for preventing external light from being input to the first switching transistor ST1, second switching transistor ST2, and driving transistor DT of the pixel circuit unit CA. That is, the light blocking layer 20 covers the pixel circuit unit CA.
However, in the related art organic light emitting display device, a characteristic deviation of a threshold voltage “Vth” of a driving transistor occurs in each pixel due to a process differential, and a plurality of the driving transistors are deteriorated at different speeds when the related art organic light emitting display device is driven for a long time. The deterioration of the plurality of the driving transistors causes a quality of an image to be degraded.